An exhaust aftertreatment device that purifies nitrogen oxides (NOx) contained in exhaust gas of an engine with a selective catalytic reduction (abbreviated as “SCR” hereinafter) has been known. Urea aqueous solution injected by an injector is supplied to the SCR. The injector is attached as a component of a mixing device provided upstream of the SCR (see, for instance, Patent Literatures 1 and 2). The urea aqueous solution is injected from the injector to exhaust gas flowing through the mixing device to mix the urea aqueous solution with the exhaust gas within the mixing device. As a result, the urea aqueous solution is thermally decomposed by the heat of the exhaust gas to produce ammonia. The ammonia is used as a reductant in the SCR.
It should be noted in Patent Literatures 1 and 2 that the injector for injecting the urea aqueous solution is attached near an upstream end of the mixing device. Accordingly, a urea aqueous solution pipe connected to the injector extends from the injector along an extension of an axial line of a straight pipe as a part of the mixing device. In the above, when the exhaust aftertreatment device is to be disposed in a limited space (e.g. an engine room) as in a construction machine, the urea aqueous solution pipe extending from the injector interferes with a wall face of the engine room. Thus, in a typical arrangement, the urea aqueous solution pipe is jointed to the injector with the use of an elbow pipe at a position close to the injector, so that the urea aqueous solution pipe is bent approximately at a right angle to be housed within the engine room.